The present invention relates to a transparent rear projection screen of the kind comprising a sheet-shaped Fresnel lens and a picture-forming sheet-shaped screen mounted in front of the Fresnel lens (as viewed by the watcher or watchers). The back of the screen has vertical, backward convex lenses which are situated vertically in the working position of the screen, and vertical masking strips on its front which are interspaced by strip-shaped sections positioned opposite to the backward convex lenses, each of these last-mentioned lenses being designed in such a way as to refract the light rays from the Fresnel lens which hit them so that these rays are emitted through the strip-shaped sections.
Such a screen is disclosed in Danish patent application No. 4725/83 filed in the name of Dai Nippon Insatsu Kabushiki Kaisha, Japan, in which priority is claimed from Oct. 15, 1982 (Japanese application No. 180790/82), Oct. 15, 1982 (Japanese application No. 155928/82), and Dec. 3, 1982 (Japanese application No. 183175/82).
Such a screen has the effect that the backward convex lenses of the picture-forming screen focus all the rays coming from the Fresnel lens on the strip-shaped sections so that loss of light is avoided and a strongly luminous picture is thus obtained. The masking strips provide the screen with a good contrast effect since to a great extent they prevent ingress of disturbing light from the front into the picture-forming screen.
In order to improve the picture resolution or definition capability of such screens it is desirable to reduce the pitch of the screen which in this case means the distance between the central axes of two adjacent masking strips, or in other words the distance between the apices of two adjacent backward convex lenses. In order to reduce this pitch it is necessary that the lenses facing backward are designed with a correspondingly reduced focal length since if not they will be unable to focus all the light on the strip-shaped sections. In order to reduce this focal length the curvature of the lenses facing backward has to be increased, with the effect that their side edges will be prositioned closer to the front of the picture-forming screen. Hence deep notches will, however, be formed between the backward convex lenses, and as the screen is already very thin, the effect will be a higher risk of rupture when the picture-forming screen is handled, especially due to the notch sensitivity which is aggravated further by the fact that screens of this nature are relatively large (approx. 1 m.sup.2).
It is an objective of the present invention to provide a screen of the kind referred to above with a high picture resolution or definition capability and where such a notch sensitivity is avoided by maintenance of a relatively small screen thickness.